This invention relates to a method of fabricating a vertical cavity surface emitting laser which is capable of emitting long-wavelength light and to the vertical cavity surface emitting laser.
Vertical cavity surface emitting lasers (VCSELs) include first and second distributed Bragg reflectors (DBRs) formed on opposite sides of an active area. The VCSEL can be driven or pumped electrically by forcing current through the active area or optically by supplying light of a desired frequency to the active area. Typically, DBRs or mirror stacks are formed of a material system generally consisting of two materials having different indices of refraction and being easily lattice matched to the other portions of the VCSEL. In conventional VCSELs, conventional material systems perform adequately.
However, new products are being developed requiring VCSELs which emit light having long-wavelengths. VCSELs emitting light having long-wavelengths are of great interest in the optical telecommunications industry. This long-wavelength light can be generated by using a VCSEL having an InP based active region. When an InP based active region is used, however, the DBRs or mirror stacks lattice matched to the supporting substrate and the active region do not provide enough reflectivity for the VCSELs to operate because of the insignificant difference in the refractive indices between the two DBR constituents.
Dielectric mirror stacks can be used for VCSEL applications, but they suffer from poor thermal conductivity. Since the performance of these long-wavelength materials is very sensitive to temperature, the thermal conductivity of the DBRs is very important.
Accordingly it is highly desirable to provide a method of fabricating long-wavelength VCSELs with good thermal conductivity.
It is an object of the present invention to provide new and improved methods of fabricating long-wavelength vertical cavity surface emitting lasers.
It is another object of the present invention to provide new and improved methods of fabricating long-wavelength vertical cavity surface emitting lasers in which materials with good thermal conductivity and refractive indices are used.
It is still another object of the present invention to provide new and improved long-wavelength vertical cavity surface emitting lasers.
It is a further object of the present invention to provide new and improved long-wavelength vertical cavity surface emitting lasers incorporating materials with good thermal conductivity and refractive indices.
It is yet a further object of the present invention to provide new and improved long-wavelength vertical cavity surface emitting lasers which can be either optically or electrically pumped.
A long-wavelength VCSEL is disclosed with a novel method of fabrication. The VCSEL includes a long-wavelength active region epitaxially grown on a compatible substrate with a high heat conductivity distributed Bragg reflector (DBR) mirror stack metamorphically grown on the active region. A supporting substrate is bonded to the DBR mirror stack and the compatible substrate is removed. A second mirror stack, either a DBR or a dielectric mirror stack, is formed on the opposite surface of the active region. The supporting substrate can be, for example, a thick metal layer deposited on the DBR or a second semiconductor type of substrate. The DBR and second mirror stack are preferably formed of materials with good thermal conductivity and refractive indices.
In a preferred embodiment, an indium phosphide (InP) active region is grown on an InP based substrate and an AlAs/GaAs based metamorphic DBR mirror stack is epitaxially grown on the active region. AlAs/GaAs has good thermal conductivity and sufficiently different refractive indices to produce a good mirror stack. The supporting substrate may be either a mechanical InP based substrate bonded to the active region or a layer of plated metal, such as copper, silver, gold, nickel, aluminum, etc. The plated metal supporting substrate provides additional thermal conductivity for the VCSEL.